Means for preconditioning and deposition of coating material



Sept. 1, 1964 J. SEDLACSIK, JR 3,147,146

MEANS FOR PRECONDITIONING AND DEPOSITION OF COATING MATERIAL Filed Feb. 2, 1961 INVENTOR JOHN SEDLACSIK JR.

ATTORNEY United States Patent '0 3,147,146 MEANS FGR PRECQNDITIONING AND DEPOSI- TION F CUATKNG MATERIAL John Sedlacsik, 'Jr., 111 Monroe St, Garfield, NJ. Filed Feb. 2, 1961, Ser. No. 86,812 7 Claims. (Cl. 118-627) This invention relates to new and useful method and means for applying fluent coating material to an article or object to be coated by a plurality of preconditioning steps of the coating material prior to final atomization thereof, which is preferably followed by electrostatic deposition of the atomized material, and is a continuationin-part of my copending application Serial No. 627,- 813, filed December 12, 1956, now abandoned, for Spray Device With Supersonic Means.

An object or feature of the invention is to precondition the coating material by subjecting same to supersonic vibrational waves or shock waves and thereafter atomizing the material by centrifugal atomization, and providing deposition preferably by electrostatic means.

Another feature of the invention is to provide preconditioning of coating material by subjecting same to a multiplicity of preconditioning steps, such as pressure spraying of the coating material onto an atomizing head, and subjecting said coating material on the atomizing head to ultrasonic action' and further feeding the coating material by action of ultrasonic vibrational or shock waves, which may result in simple agitation and/ or cavitation resulting in atomization of the coating material simultaneous with the final atomization. The above may be simultaneous with atomization by centrifugal action after the coating material has been deposited on the surface of a centrifugal atomizer.

A further feature ofthe invention is to provide a 360 pressure sprayingapparatus or nozzle coating an inner surface of an atomizer head and simultaneously subjecting said atomizer head to ultrasonic energy, which may be subsonic or supersonic in frequency for the purpose of preconditioning the coating material. The coating material is ultimately atomized from the atomizer head array and is preferably deposited by electrostatic deposition but may be deposited by a combination of centrifugal action and electrostatic forces.

The invention contemplates preconditioning of the coating material by'subjecting same to ultrasonic and pressure action prior to a final atomization by centrifugal action, and wherein the deposition may be either wholly or in part by either centrifugal force or electrostatic force or a combination of both centrifugal and electrostatic action.

When pressure spraying is utilized as a preconditioning step for utilization of the coating material, the pressure action may be either hydraulic or pneumatic and will generate a spray of fine particles preferably disposed in a radially projected spray 360 about the axis of the atomizer. The material sprayed from the pressure nozzle will be fundamentally sprayed onto the surface of a centrifugal atomizer wherein the coating material is ultimately sprayed therefrom by centrifugal force.

The invention relates to the formation of a spray from a liquid material capable of relatively rapid atomization by expelling same from the issuing source where the material is held in the liquid form through the use of a motive agent, such as air or hydraulic force, in conjunction with an electrostatic influence, and finally discharging the spray from the sharp edge of a supersonically vibrating disc, directly upon the object to be sprayed.

This invention is directed to means for improving agitation, dispersion, atomization and deposition of the atomized particles employing a charged field head or gun ice mechanism upon an oppositely charged article, such means providing greater stabilityto the projected spray or jet and imparting a sharper edge definition to the issuing pattern.

Transducers of the piezo-electric type, for example, transform electricaldriving energy into sound energy. Here the mechanical vibratory motion is obtained by impressing an electric charge across a slab. of a crystalline material such as quartz, barium titanate, Rochelle salts, ammonium dihydrogen phosphate or ferroceramics.

Barium titanate is one of a family of artifically produced piezo-electric materials finding numerous applications in ultrasonics and its use is contemplated herein, although any other suitable material, such as one of those above enumerated, may be employed in lieu of said barium titanate, including metallic core type transducers made up, for example, to include laminations of nickle metal.

Waves from a piezo-electric crystal or the like transducer, for example, exert a unidirectional mechanical pressure whereby the waves generated act upon the surface of a liquid. Strong supersonic motions or waves in a liquid, as the waves arrive at an exposed surface, are rectified or converted into motions of the main body of the liquid whereby supersonic waves may be used to cause unidirectional movement or flow of liquids, which unidirectional flow may be modulated by modulating the strength or frequency of the waves. Cavitation or agitation with pressure spraying for further atomization is frequently desired as a preconditioning step of the coating material prior to the sequential or final atomization of the coating material prior to deposition of the atomized coating material.

While the preconditioning set forth herein specifically refers to a final atomization by centrifugal action, it is to be understood that any of the preconditioning steps of the coating material employed in conjunction with the rotating disc is contemplated by the subjoined claims, since it is understood that merely rotating the disc at a slower speed to avoid good or commercial centrifugal atomization, will not avoid the concept of the invention. In other words, while the invention specifically refers to centrifugal atomization as a final atomization, it is to be understood that the preconditioning steps of the invention may be employed with a more slowly rotating disc which may result in electrostatic atomization or perhaps a combination of electrostatic atomization and poor centrifugal atomization. It is to be understood that the invention is not limited to centrifugal atomization but rather any form of final atomization combined with one or more of the preconditioning steps including ultrasonic agitation of an annular pattern of the disc either independently or in conjunction with the pressure spray nozzle. Therefore, the invention may utilize ultrasonic agitation of the coating material which will, under suitable conditions, cause some cavitation 360 about the surface of the atomizer head and resulting in some 360 ultrasonic atomization which may be used independently of the annular atomizing edge of the head or in combination therewith so that part of the material may be ultrasonically atomized in 360 form and used in conjunction with the remainder of the material being centrifugally or electrostatically atomized.

A novel apparatus is provided herein for the spraying of a liquid material in a fine, mist-like jet in response to the force of supersonic vibrational waves which are caused to act upon an exposed surface of the liquid, which is at this instant in the form of a very thin film.

A source of electrostatic high potential, having one terminal grounded and its opposite terminal connected to the atomizing head of the spray gun, creates a strong electrostatic field between the head and the article to be coated, which article is also grounded.

The force of this field by itself transforms the coating material into a spray of fine, charged particles and creates an attraction sufiicient to pull the spray to the grounded article, which force is strengthened by the supersonic compressional waves which may be applied to the surface of the liquid as it moves in a thin film toward the discharge edge of the apparatus for formation of the liquid into a fine, mist-like spray which is extremely desirable in electrostatic spraying.

Energy imparted to a liquid by ultrasonic excitation, no matter how strong, will not cause the liquid to break into a mist unless the cavitation threshold is exceeded. High electrostatic stresses on the surface of the liquid may reduce this cavitation threshold, but the cavitation process produces the mist, not the compressional waves nor the unidirectional motion in the liquid.

The unidirectional flow in the liquid may be used to advantage as applied herein, producing a mixing action to prevent a non-uniform distribution of paint or the like on a fiat surface. In this case, it would counteract the tendency of the paint to break up under high electrostatic stress into small drops as a result of the mutual repulsion of small particles with like charges. However, concentric rings of paint would still occur at the nodal points of standing waves produced on the vibrating surface.

To produce the fine mist at cavitation levels, the high intensity of sound must be concentrated at a point or a thin line by some acoustical focusing device. At low ultrasonic frequencies this can be accomplished with a horn or velocity transformer. At high ultrasonic frequencies, the transducer can be shaped into a usually spherical concave surface to focus the sound at the surface of the liquid in which it is immersed.

When cavitation occurs, small vapor-filled bubbles are formed in the liquid, and these bubbles collapse or implode. The shock waves thus generated set up large disruptive forces at the surface which causes the liquid to break up into a fine mist.

In this invention, the coating material is normally supplied to the discharge spout and its region of corona discharge at a rate at which it can be electrically atomized by the corona discharge most efficiently and effectively, after which the charged particles are projected in spray form upon a supersonically vibrating disc-like element from which they are subsequently discharged toward the oppositely charged article or target.

Depending upon the viscosity and other characteristics of the material, and depending also upon the rate at which the sprayer is modulated so that the unidirectional flow is accordingly modulated, the control of the supply is such as to permit the discharge of precisely the correct quantity and size of particles so as to effect the greatest efficiency in coating a surface.

The foregoing and other objects and advantages of the invention will appear morefully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawing wherein an embodiment of the invention is illustrated. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description, and is not to be construed as defining the limits of the invention.

The figure is a diagrammatic view of apparatus embodying the novel features of the invention.

In this drawing, I have illustrated a complete example of one physical embodiment of the invention. It will however be understood that changes and alterations are contemplated and may be made within the scope of the claims, without departing from the basic principles of the invention.

Referring now to the drawing more in detail, and more particularly to the preferred form of my invention selected for illustrative purposes, I have shown a shell represented d by 482, which is secured to a centrally positioned shaft 4&4.

A nozzle is shown at 406 for the delivery of a motive agent, such as air, and a fluent coating material, such as paint, to the apparatus.

Such a nozzle may be of any desired form, that shown for purposes of disclosure being similar to the nozzle of the US. patent application of John Sedlacsik, Serial Number 481,532, filed January 13, 1955, now abandoned.

The fluent coating material is led from a source (not shown) to the rear end of the nozzle 466 and likewise the motive agent is led from a source (not shown) to the rear end of the nozzle 4%.

Resilient O-rings 403 are disposed between the nozzle 406 and the shell 402, with a hollow spacer 410 provided therebetween.

A piezo-electric crystal is represented by C and may consist of one of the crystalline materials such as quartz, barium titanate, Rochelle salt, or the like, although it will be understood that barium titanate is preferred. Desirably, the crystal will be of a type having a natural frequency of between 10 kilocycles and 40 megacycles.

A ring 412 electrically connected to one side of the crystal C is electrically insulated from the shell by an insulating washer 414.

A member 416, which for purposes of disclosure is shown as being disc-shaped, is electrically connected to the nozzle 406 and to the other side of the crystal, as at 413 and 420.

The shaft 404, the shell 402, the crystal C, and the disc 416 are rotated as a unit.

The fiuent coating material and the motive agent are discharged radially from the forward end of the nozzle as indicated by 422. The coating material is discharged onto the inner face of the disc, where centrifugal force spreads it outwardly in an ever thinning layer to the knife edge of the disc.

As the streams of liquid and air pass outwardly from the nozzle, the same are subjected to the atomizing effect of the corona discharge from the electrode whereby the finely divided particles comprising the spray are each imparted electrical charges of like polarity. A halo effect is attained thereby. With voltage applied directly to the spray head structure, a corona discharge is formed in the region around the lips and adjacent the outermost periphery thereof, which is of an intensity sufiicient to atomize into particulated form the coated material being discharged from the nozzle and to project the coating material in spray form toward the surface of the disc.

That is to say, in actual operation, the electrical energy is maintained at the high potential nozzle or spray assembly. The coating material being atomized and the motive agent are delivered through the respective delivery tubes and connections to the head assembly. The coating material and motive agent are released in the form of high velocity streams where they meet and mix with each other under pressure and are atomized and electrically charged passing outwardly onto the disc with high turbulence.

The rotation of the disc causes the coating material to traverse the disc outwardly radially thereof to its peripheral edge 424.

The edge 424 of the disc, according to the invention is knife-like in its cross-section. Normally, coating material would be discharged by the edge of the disc during the rotation thereof, and the supersonic vibration of the edge of the disc renders the discharge extremely fine in nature, similar to a mist or fog.

A rectifier-power-supply is represented by R which has its input connected to an alternating line, of say volts, which is represented by 426.

Said rectifier-power-supply is of a type well known in the art and is adapted to provide a direct current output of one-hundred-thousand volts more or less.

An oscillator of well known form has an input connected to the line 426, as by connections 428. The output of the oscillator is connected to the primary of an impedance matching transformer T, as shown.

The rectifier-power-supply, the oscillator and the transformer may be disposed within an enclosure 430 which may preferably contain oil.

The positive of the rectifier is connected to the enclosure, and the ground, by 432, as indicated. The negative of the rectifier is connected by 434 to the shaft 404, and thereby to the nozzle 406, the disc 416, and to one side of the crystal C.

One end of the transformer secondary is connected by wire 436 to a brush or contact 438 having a wiping contact with the ring 412 which ring is electrically connected to the other side of the crystal.

An article for receiving coating material is represented by A, and is connected to ground, as shown.

In operation, the oscillator, being connected through the transformer T by connections 436, 44% and 434 to opposite sides of the crystal C, activates said crystal to oscillation at its natural frequency which preferably will be in the order of a thousand megacycles.

The Crystal C brings about vibrations of the disc at its frequency and at a low amplitude, which results in the coating material at the knife-like peripheral edge of said disc being broken up into an extremely fog-like mist.

In addition to piezo-electric means for producing the ultrasonic energy herein employed, the magnetostrictive, electrodynamic, fluid dynamic and hydrodynamic oscillator systems could be likewise employed so as to accomplish the results herein recited.

The piezo-electric, magnetostrictive, and electrodynamic systems can actually be coupled to the device as shown. The other two aforementioned systems are means of imparting ultrasonic energy to the vapor or liquid phase by a jet or whistle action in the fluid or vapor, both of which can be used in this process by suitable adaptions easily envisaged by one skilled in this art.

While an embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes may also be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. Apparatus for electrostatically coating articles comprising a disc, nozzle means for feeding coating material at a controlled rate to the inner surface of said disc, means to uniformly distribute coating material over a 360 degree surface of said disc to form a film thereon, means for vibrating said film to provide cavitation thereof for atomization of said film of coating material, and means for establishing an electrostatic field between said atomized material and said articles for electrostatic deposition of said atomized material.

2. Apparatus for electrostatically coating articles, comprising disc-type atomizer means for receiving a coating material, means for establishing an electrostatic field between said atomizer means and said articles for electrostatically depositing atomized coating material on said articles, said atomizer means including spray nozzle means having a nozzle end disposed within the confines of said atomizer means and adapted initially to spray said coating material 360 degrees onto said atomizer means for fluid-pressure dispersion of said coating material in the form of a film on said atomizer means preliminary to providing final atomization and deposition of said initially sprayed coating material from said atomizer means onto said articles, vibrational means for vibrating said atomizer means at ultrasonic frequency to provide ultrasonic atomization of said film of coating material, said vibrational means including an ultrasonic transducer afiixed to said disc-type atomizer, and an ultrasonic frequency generator coupled to said vibration means.

3. Apparatus for electrostatically coating articles, comprising a disc-type atomizer head for receiving a coating material, means for establishing an electrostatic field between said atomizer head and said articles for electrostatically depositing said coating material on said articles, said atomizer head including spray nozzle means having a nozzle end disposed within the confines of said atomizer head and adapted initially to atomize and spray said coating material 360 degrees onto said atomizer head for fluid-pressure dispersion of said coating material in the form of a film on said atomizer head preliminary to providing final atomization and deposition of said initially sprayed coating material from said atomizer head onto said articles, and frequency responsive transducer means for oscillating said film to provide cavitation thereof for atomization of the coating material prior to electrostatic deposition.

4. Apparatus for electrostatically coating articles, comprising a disc-type atomizer head for receiving a coating material, means for establishing an electrostatic field between said atomizer head and said articles for electrostatically depositing atomized coating material on said articles, spray nozzle means adapted intially to spray said coating material onto said atomizer head for fluid-pressure dispersion of said coating material in the form of a film on said atomizer head preliminary to providing final ultrasonic atomization and electrostatic deposition of said initially sprayed coating material from said atomizer head onto said articles, and vibrational means for vibrating said atomizer head at ultrasonic frequency to provide said ultrasonic atomization of said film of coating material prior to deposition.

5. Apparatus for electrostatically coating articles as set forth in claim 4, and wherein said vibrational means includes a cylindrical shaped piezo-electric crystal aifixed to said atomizer head and electric circuit means coupled to said piezo-electric crystal for generating a frequency in the ultrasonic range.

6. Apparatus for electrostatically coating articles as set forth in claim 2, and wherein said disc-type atomizer head is rotatable at a speed sufficient to provide centrifugal atomization of coating material from the peripheral edge of said disc-type atomizer head remaining on said atomizer head after being agitated by said ultrasonic means.

7. Apparatus for electrostatically coating articles as set forth in claim 4, and wherein said disc-type atomizer head is rotatable at a speed sufficient to provide centrifugal atomization of coating material from the peripheral edge of said disc-type atomizer head subsequent to periodic agitation of the coating material during the interval of ultrasonic atomization.

References Cited in the file of this patent UNITED STATES PATENTS 

1. APPARATUS FOR ELECTROSTATICALLY COATING ARTICLES COMPRISING A DISC, NOZZLE MEANS FOR FEEDING COATING MATERIAL AT A CONTROLLED RATE TO THE INNER SURFACE OF SAID DISC, MEANS TO UNIFORMLY DISTRIBUTE COATING MATERIAL OVER A 360 DEGREE SURFACE OF SAID DISC TO FORM A FILM THEREON MEANS FOR VIBRATING SAID FILM TO PROVIDE CAVITATION THEREOF FOR ATOMIZATION OF SAID FILM OF COATING MATERIAL, AND MEANS FOR ESTABLISHING AN ELECTROSTATIC FIELD BETWEEN SAID ATOMIZED MATERIAL AND SAID ARTICLES FOR ELECTROSTATIC DEPOSITION OF SAID ATOMIZED MATERIAL. 